The Victorian police union is outraged at the use of taxpayers' money to sue the force after a protester was dribbled on by a police horse.

The Flemington and Kensington Community Legal Centre has reportedly launched the case on behalf of two protesters who took part in a demonstration at the Maribyrnong Immigration Detention Centre in 2011.

They were protesting with the the Refugee Action Collective.

One of the protesters claims a horse salivated on him, while the second protester alleges a horse stood on his foot when he fell to the ground while being pushed by police on horseback.

The Police Association's Bruce McKenzie says the lawsuit is outrageous.

"Taxpayers ought to be outraged that their money is being used for legal action for purposes related to a police horse dribbling," he said.

"Come on, give us a break."

He says the Association respects the rights of people to demonstrate, but says there is a tendency at some protest for a 'lunatic fringe' to become involved.

"The situation at public demonstrations can become quite volatile, and it is a difficult job for the police to patrol some of these protests or demonstrations, and that's made more difficult when people allegedly taking part in a peaceful protest, turn violent," Mr McKenzie said.

He says the public's right to protest is undermined when police are put at risk.

"There is evidence that in this case, the police horse was put at risk of injury," he said.

'Weapons of war'

The Chief executive of the legal centre, Anthony Kelly, says the two people injured in the 2011 protest are Alexander Forbes and Mark Ryan.

"The problem has been the use of police horses as a form of crowd control," he said.

"We want to focus around the use of police horses.

He says there is really no safe way to use police horses in a crowd.

"Police horses were being used to push, to contain, to create a barrier," he said.

"Essentially to intimidate and confine the protesters."

Mr Kelly says the legal action is essentially a test case in relation to the use of police horses at demonstrations.

"There's been no real case that has challenged the use of police horses, for some decades," he said.

"Even more worryingly, there's been no parliamentary scrutiny or regulation on the use of police horses, in living memory."

Mr Kelly says horses can be dangerous weapons.

"They've being used as weapons of war,"

"There's a long history on the use of police horses.

"But today they're an anachronism."

He says horses should not be used as a crowd control tool.

"The officers on top of the horses can't use batons safely, they can't use tasers or anything else safely," he said.

Writ alleges assault and unlawful battery

The writ obtained by the ABC alleges Mr Forbes who aged 18 at the time, was in fear of being trampled or bitten by the horse.

It also alleges he was frightened and intimidated by the horse.

The second man hurt in the incident is now 50 years of age.

The writ alleges he was pushed by police on horseback.

It is also alleged the horse tread on his foot when he fell to the ground.

Both were transported to different hospitals with various injuries.

They are claiming damages for pain, suffering, loss and damage.

"It a very easy way to trivialise these sort of things but one received a broken clavicle," said Mr Kelly.

"Their right clavicle was fractured in the incident where a horse rolled on top of him.

"The other plaintiff had a police horse stand on his foot causing soft tissue damage. He was on crutches for the better part of a month."

Mr McKenzie says police were just doing their job.

"The Police Association and our members are outraged that public funds can be used for the purpose of taking some form of action against our members for doing no more or less than their job," he said.

Liana Buchanan from The Federation of Community Legal Centres says the civil action is legitimate.

"I think it’s underplaying the allegations to suggest that it’s just about horse dribble," she said.

"Just on the material that is in the public domain there’s clearly allegations of injury and other force being used and again I think it probably is appropriate for the use of horses to be considered in these cases."